the invention relates to a printhead suitable for use with image forming systems and more particularly relates to a coplanar arrangement of electrodes within a single dielectric layer of the printhead.
many different printing technologies today utilized in image forming systems create and reproduce images in different ways. A process executed by some of these technologies (e.g.,Electron Beam Imaging) includes a step of charging a surface of an image-receiving member, such as a drum, with a latent charge image. The term image-receiving member include a drum, flat or curved surfaces, or a flexible belt. The image-receiving member can also be a liquid crystal or phosphor screen, or similar display panel in which latent charge image results in a visible image. Typically, an exterior surface of the image-receiving member includes a material, such as a dielectric include glass enamel, flame or plasma sprayed high-density aluminum oxides, and plastics, including polyamide, nylon, and other tough thermoplastic or thermoset resins, among other materials.
The image-receiving member, or drum, moves past an image forming device, such as printhead, which produces a stream of accelerated electrons as primary charge carriers. The electrons reach the drum, landing in the form of a latent charge image. The latent charge image then receives a developer material, to develop the image, and the image is then by press or electrostatic transfer applied and fused to a medium, such as a sheet of paper, to form a printed document.
The printhead most often includes a film having a multi-electrode structure that defines an array of charge generating sites. Each of the charge generating sites, when the electrodes are actuated, generates and directs toward the drum a stream of charge carriers, e.g., electrons, to form a pointwise accumulation of charge on the drum that constitutes the latent image. A representative printhead generally includes a first collection of drive electrodes, e.g., RF-line electrodes, oriented in a first direction across the printing process direction. A second collection of control electrodes, e.g., finger electrodes, oriented transversely to the drive electrodes, forms cross points or intersections with the drive electrodes constituting an array of charge generating sites at which charges originate. A dielectric layer couples to, and physically and electrically separates and insulates, the RF-line electrodes from the finger electrodes.
The printhead can also include a third electrode structure, often identified as a screen electrode. This screen electrode couples to the finger electrodes by an insulating structure, such as a spacer layer. The screen electrodes have a plurality of passages aligned with the charge generating sites, to allow the stream of charge carriers to pass through. The screen electrode can be a single conductive sheet having an aperture aligned over each charge generation site. Polarity of charge carriers passing through the passages, or apertures, depends on the voltage difference applied to the finger and screen electrodes. Polarity of particles accumulated on the drum to create latent image is determined by the voltage difference between the screen electrode and the drum surface. The charged particles of appropriate polarity are inhibited from passing through the aperture, depending upon the sign of their charge, so that the printhead emits either positive or negative charge carriers, depending on its electrode operating potentials.
A typical structure of the printhead is a vertical arrangement, wherein the RF-line electrodes, dielectric, finger electrodes, spacer, and screen electrode are gradually laminated each on top of the other. This vertical structure for a thin film printhead leads to a relatively high capacitance of the RF-lines. The large capacitance limits the usable charge generating frequency and consequently the speed of printing.
There exists in the art a need for a low capacitance printhead. The printhead of the present invention includes a first plurality of electrodes (e.g., RF-line electrodes), and a second plurality of electrodes (e.g., finger electrodes), arranged in a substantially common plane. A subsequently deposited dielectric layer seals the coplanar first plurality of electrodes and isolates electrical connections to the second plurality of electrodes.
Each of the plurality of electrodes has a different arrangement, according to a further aspect of the present invention. One such arrangement includes electrodes with an elongate section having electrode peninsulas extending outwardly therefrom. The other plurality of electrodes includes individual electrodes surrounding each of the extending electrode peninsulas. A single dielectric layer then seals the substantially coplanar electrode layers.
The single dielectric layer, according to one aspect of the present invention, can be made of two or more layers, each layer being formed of a different material.
A method of making a printhead according to the teachings of the present invention includes applying a metal coating to a substrate material to form electrodes. An etching process forms two sets of substantially coplanar electrodes from the substrate coating material. A dielectric composition then covers each of the two sets of electrode patterns. The dielectric composition is then selectively perforated and a second metal layer is deposited to form electrode interconnections.